Re: Incorrect Tyre Size.....Or Not
Mixing widths front to rear probably isn't ideal but don't think for a minute that a change from 215s to 225s will turn your car into some wild oversteering monster.
Bear in mind that a 225 is only 10mm wider than a 215. Different makes of tyre have different size footprints and different levels of grip anyway. Different levels of wear will also affect the level at each end depending on whether it is wet or dry. If you have super sticky track day 225s on the front and knackered Korean remould 215s on the back it might be a bit twitchy but with decent tyres all round, that 10mm won't make a noticeable difference n the real world unless you are actually Lewis Hamilton and drive everywhere right on the ragged edge. If that's the case, get McClaren to buy you a new set all round.
If you only need two new tyres and want to get back to the original size put the new wider ones on the back and then replace the fronts when they need it.